This proposal is primarily a clinical study to assess the value of circulating stem cells as a means to reconstitute the bone marrow of patients at risk from myelosuppression. The main objective is to investigate procurement, preservation, and transfusion of peripheral blood mononuclear cells containing CFU-C and pleuripotential stem cells. The long range goal is to offer the opportunity for delivering increased and presumably more effective chemotherapeutic drug regimens that could result in a greater antitumor response in patients with cancer. Expression of CFU-C is controlled by inhibitory and stimulatory substances and influenced by complex cell interactions. Quantitation of CFU-C in normals and patients therefore requires investigation of highly purified cell populations. Experimental animal models are used to provide preclinical data. The results of these studies will lead to an assessment of the value of autologus stem cell support in reducing morbidity associated with intensive antitumor therapy.